Rainbow-electronics ATmega128L Manuel d'utilisateur télécharger pdf (Page 248)

248

ATmega128(L)

2467B–09/01

Scanning the Digital Port Pins Figure 123 shows the Boundary-scan Cell for a bidirectional port pin with pull-up func-

tion. The cell consists of a standard Boundary-scan cell for the Pull-up Enable – PUExn

– function, and a bidirectional pin cell that combines the three signals Output Control –

OCxn, Output Data – ODxn, and Input Data – IDxn, into only a two-stage shift register.

The port and pin indexes are not used in the following description

The Boundary-scan logic is not included in the figures in the Data Sheet.

Figure 124

shows a simple digital Port Pin as described in the section “I/O-Ports” on page 60. The

Boundary-scan details from

Figure 123 replaces the dashed box in Figure 124.

When no alternate port function is present, the Input Data – ID corresponds to the PINxn

ister, Output Control corresponds to the Data Direction – DD register, and the Pull-up

Enable – PUExn – corresponds to logic expression PUD

· DDxn · PORTxn.

Digital alternate port functions are connected outside the dotted box in

Figure 124 to

make the scan chain read the actual pin value. For Analog function, there is a direct

connection from the external pin to the analog circuit, and a scan chain is inserted on

the interface between the digital logic and the analog circuitry.

Figure 123. Boundary-scan Cell for Bidirectional Port Pin with Pull-Up Function.

DQ DQ

Port Pin (PXn)

VccEXTESTTo Next CellShiftDR

Output Control (OC)

Pullup Enable (PUE)

Output Data (OD)

Input Data (ID)

From Last Cell

UpdateDRClockDR

FF2 LD2

FF1 LD1

LD0FF0

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Rainbow-electronics ATmega128L Manuel d'utilisateur Page 248